This invention relates to encapsulation of integrated circuit chips which are bonded to a metallized insulation substrate primarily for the purpose of mounting or inclusion as part of a hybrid integrated circuit.
In semiconductor technology, integrated circuit chips are bonded to metallized substrates for mounting purposes, as in dual in-line packages, or for inclusion as part of a hybrid integrated circuit which includes many chips and thin film elements. In order to protect such chips from moisture, particulate matter, and damage during assembly, it is usually necessary to apply some form of encapsulant. A suitable form of encapsulating material for such uses has been found to be RTV (Room Temperature Vulcanizing) silicone compounds which are characterized by their curing (crosslinking) as the result of reaction with moisture in the air to form a silicone elastomer or rubber. In order to permit the RTV silicone compound which is in the form of a paste, to be applied by standard flow-coating techniques, it is usually diluted with a suitable solvent to form a dispersion of the desired viscosity. After application, the encapsulant is usually cured at room temperature in an ambient which permits crosslinking.
Use of such encapsulants has generally been satisfactory. However, when beam-leaded chips are bonded to substrates, the chip is slightly raised above the substrate and complete filling of thes gaps under the chips by the encapsulant becomes important for complete protection. Complete under-chip filling has been found to be a problem with encapsulants using standard curing procedures, especially in view of the increasing size of chips needed for sophisticated applications such as memories. Typically, for square chips no greater than about 0.060 inches on a side, complete filling is consistently obtained with commercially available RTV dispersions using standard solvent removal and curing techniques. However, for square chips measuring about 0.080 inches on a side or greater, complete under-chip filling typically cannot be consistently obtained with commercially available RTV dispersions using standard techniques.
It is therefore a primary object of the invention to provide a method of encapsulating beam-leaded integrated circuit chips which results in complete filling under the chips even for large area chips.